Foamable external compositions cause less stress on skin upon application, and can be uniformly applied over a wide area. Therefore, they are widely used in cosmetics and pharmaceutical products (see Patent Documents 1 and 2). However, use of liquefied gases such as LPG and fluoroalkane, which had been predominantly used with foamable external compositions, is now restricted due to the ozone hole problem and others. In addition, there is a concern about irritation due to the gas dissolved in the foam. For these reasons, liquefied gases are now becoming less practical. Accordingly, no-gas formulations with which pump foamers are used are emerging to replace the conventional products (for example, see Patent Documents 3 and 4).
Compositions for pump foamers have been under extensive studies in the field of cleaning agents and the like. According to these studies, combined uses of a nonionic surfactant with mainly an anionic surfactant and an amphoteric surfactant which are excellent in foaming and foam stability are widely explored (see Patent Document 5). However, irritability to mucous membrane and skin becomes an issue when an anionic surfactant and an amphoteric surfactant such as fatty acid soaps having high surface activity effects are formulated. On the other hand, use of a nonionic surfactant, which has a low skin irritability, can not provide sufficient foaming, foam stability, and foam quality may not be obtained due to its low foamability (see Patent Document 6). Further, the aforementioned irritability to mucous membrane and skin is a more serious issue for a cosmetic or medical composition for pump foamers which is used without being washed-off. This is because a component responsible for skin irritation may not be removed by washing. For these reasons, there have been demands for developing a safe composition for screen foamers such as a composition for pump foamers. That is, a foaming means with less irritability for an external composition for screen foamers has been desired.
However, an external composition for screen foamers comprising a less irritating nonionic surfactant as a foaming component has not yet been known, and any attempt has not been tried to formulate such a composition in view of the low formability of nonionic surfactants.